U.S. patent number 4,322,713 [Application Number 06/128,434] was granted by the patent office on 1982-03-30 for level monitoring methods and apparatus particularly for high-resistivity liquids.
Invention is credited to Rino Ammenti, Sherman W. Duck.
United States Patent |
4,322,713 |
Duck , et al. |
March 30, 1982 |
Level monitoring methods and apparatus particularly for
high-resistivity liquids
Abstract
An electronic dipstick or similar probe has an electrically
insulated conductor which is diminished or otherwise adjusted with
respect to a given point of reference and a predetermined low
liquid level. Level monitoring functions on liquids having high
volume resistivities in the megohm-centimeter range are
attainable.
Inventors: |
Duck; Sherman W. (Redwood City,
CA), Ammenti; Rino (Millbrae, CA) |
Family
ID: |
22435367 |
Appl.
No.: |
06/128,434 |
Filed: |
March 10, 1980 |
Current U.S.
Class: |
340/620;
340/450.3; 73/293 |
Current CPC
Class: |
G01F
23/24 (20130101); G01F 23/04 (20130101) |
Current International
Class: |
G01F
23/24 (20060101); G01F 23/00 (20060101); G01F
23/04 (20060101); G08B 021/00 () |
Field of
Search: |
;340/52R,52B,52F,59,612,618,620 ;73/293 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Wesley Iversen; Electronics Review; Jul. 1979; Sensors Respond to
Fluid Level; pp. 53, 54, 56..
|
Primary Examiner: Waring; Alvin H.
Attorney, Agent or Firm: Benoit Law Corporation
Claims
We claim:
1. In a method of monitoring the level of an electrically
conductive liquid in a container, the improvement comprising in
combination the steps of:
providing an elongate electric conductor with a length, relative to
a point of reference, greater than the distance between said point
of reference and a predetermined low level of said liquid;
electrically insulating said elongate conductor by providing said
elongate conductor with electric insulation for a length which,
relative to said point of reference, is greater than said
distance;
cutting said conductor and said electric insulation at said
predetermined low liquid level to diminish the length of said
insulated conductor with respect to said point of reference to a
length equal to said distance and providing said conductor at a
position corresponding to said predetermined low level relative to
said point of reference with an end free of electric
insulation;
inserting said insulated conductor of diminished length into said
container to position said free end at the location of said
predetermined low level; and
electrically monitoring the level of said liquid with said inserted
insulated conductor exposed to said electrically conductive liquid
at said free end.
2. A method as claimed in claim 1, including the step of:
adjusting the length of said insulated conductor with respect to
said point of reference to a length equal to said distance.
3. A method as claimed in claim 1, including the step of:
providing said elongate insulated electric conductor at said point
of reference with a protective tubular coating having a length
shorter than said adjusted length.
4. A method as claimed in claim 1, including the step of:
surrounding said elongate insulated electric conductor at said
point of reference with a stopper.
5. A method as claimed in claim 4, including the step of:
providing said stopper with a taper extending in the direction of
said free end.
6. A method as claimed in claim 2 wherein:
said adjusting of the length of said insulated conductor includes
the step of diminishing the length of said insulated conductor with
respect to said point of reference to a length equal to said
distance.
7. A method as claimed in claim 2, wherein:
said adjusting of the length of said insulated conductor includes
the steps of providing a movable member defining said point of
reference, and setting said movable member at said insulated
conductor at said distance from said free end.
8. A method as claimed in claim 7, including the step of:
providing said elongate insulated electric conductor with a
protective tubular coating over a range of movement of said movable
member.
9. A method as claimed in claim 2, wherein:
said adjusting of the length of said insulated conductor includes
the steps of providing around said insulated conductor a movable
stopper defining said point of reference, and setting said movable
stopper at said distance from said free end.
10. A method as claimed in claim 9, including the step of:
providing said elongate insulated electric conductor with a
protective tubular coating over a range of movement of said movable
stopper.
11. A method as claimed in claim 2, wherein:
said electrical monitoring is effected at an end of said insulated
conductor opposite said free end.
12. In a method of monitoring, with the aid of a monitoring circuit
having an input terminal and a ground terminal, the level of an
electrically conductive liquid having a volume resistivity in the
megohm-centimeter range and being located in a bottom region of an
electrically conductive container, the improvement comprising in
combination the steps of:
providing an electrically conductive tube;
electrically connecting said tube to the container and extending
said tube from the outside of the container from above said liquid
to an end of said tube inside the container;
extending an elongate electric conductor through said tube into
said liquid and providing said conductor with a free end at a
position corresponding to a predetermined low level of said
liquid;
providing said conductor with electric insulation extending along
said conductor in said tube and isolating said free end of said
conductor from said tube by extending said insulation from said
tube to below said end of said tube;
electrically connecting said input terminal to said conductor
outside of said container;
electrically connecting said ground terminal to said container;
and
supporting said monitoring circuit at an end of said elongate
electric conductor opposite said free end.
13. A method as claimed in claim 12, including the step of:
providing said elongate insulated electric conductor with a
protective tubular coating extending into said tube.
14. A method as claimed in claim 12, including the step of:
covering an end of said tube, opposite said end inside the
container, around said electric conductor.
15. A method as claimed in claim 12, including the steps of:
surrounding said elongate insulated electric conductor with a
stopper; and
inserting said stopper into an end of said tube opposite said end
inside the container.
16. A method as claimed in claim 15, including the step of:
providing said stopper with a taper extending into said tube.
17. A method as claimed in claim 15 or 16, including the step
of:
rendering said stopper adjustable relative to said elongate
electric conductor.
18. A method as claimed in claim 12, including the step of:
enclosing said monitoring circuit in a container supported at said
end of said elongate electric conductor opposite said free end.
19. In apparatus for monitoring the level of an electrically
conductive liquid in a container, the improvement comprising in
combination:
an elongate electric conductor extending into said container and
having a free end exposed to said liquid;
electric insulation covering said conductor up to said free
end;
means connected to said conductor for electrically monitoring the
level of said liquid with said conductor covered by said electric
insulation and exposed to said electrically conductive liquid at
said free end;
means for supporting said monitoring means at an end of said
insulated conductor opposite said free end; and
a container enclosing said monitoring means at said end of said
insulated conductor opposite said free end.
20. Apparatus as claimed in claim 19, including:
a protective tubular coating covering part of said electric
insulation.
21. Apparatus as claimed in claim 19, including:
a stopper surrounding said elongate insulated electric conductor
remotely from said free end.
22. Apparatus as claimed in claim 21, wherein:
said stopper has a taper extending in the direction of said free
end.
23. Apparatus as claimed in claim 21, wherein:
said stopper is adjustable along part of said elongate insulated
electric conductor.
24. Apparatus as claimed in claim 19, wherein:
said electric conductor is sufficiently stiff to carry said
monitoring means.
25. In apparatus for monitoring the level of an electrically
conductive liquid having a volume resistivity in the
megohm-centimeter range and being located in an electrically
conductive container, the improvement comprising in
combination:
an electrically conductive tube electrically connected to the
container and extending from outside of the container from above
said liquid to an end of said tube inside the container;
an elongate electric conductor extending through said tube into
said liquid and having a free end at a position corresponding to a
predetermined low level of said liquid;
electric insulation extending along said conductor in said tube and
below said end of said tube into said liquid to isolate said free
end of said conductor from said tube;
monitoring circuit means having an input terminal electrically
connected to said conductor outside of said container and a ground
terminal electrically connected to said container; and
means for mounting said monitoring circuit means on an end of said
tube opposite said end inside the container.
26. Apparatus as claimed in claim 25, including:
a protective tubular coating on said elongate insulated electric
conductor extending into said tube.
27. Apparatus as claimed in claim 25, including:
means extending around said electric conductor for covering an end
of said tube opposite said end inside the container.
28. Apparatus as claimed in claim 25, including:
a stopper surrounding said elongate insulated electric conductor
and extending into said tube at an end opposite said end of said
tube inside the container.
29. Apparatus as claimed in claim 28, wherein:
said stopper has a taper extending into said tube.
30. Apparatus as claimed in claim 28 or 29, wherein:
said stopper is adjustable along part of said elongate insulated
electric conductor.
31. Apparatus as claimed in claim 25, wherein:
said electric conductor is sufficiently stiff to carry said
monitoring circuit means.
32. Apparatus as claimed in claim 25, including: a container
enclosing said monitoring circuit means on end of said tube
opposite said end inside the container.
33. Apparatus as claimed in claim 32, wherein: said mounting means
include a tubular member surrounding part of said electric
conductor and a flange connected to said tubular member and
supporting said container.
34. An article of manufacture for monitoring the level of an
electrically conductive liquid in a container, comprising in
combination:
means for electrically monitoring the level of said liquid
including an elongate electric conductor having a length, relative
to a point of reference, greater than the distance between said
point of reference and a predetermined low level of said liquid,
being electrically insulated for a length which, relative to said
point of reference, is greater than said distance, and being
adjustable to a length equal to a distance between said point of
reference and said predetermined low level to provide an end of
said conductor free of electric insulation at said predetermined
low level of said liquid and electric monitoring circuit means
connected to an end of said conductor opposite said free end;
and
means connected to said insulated conductor for mounting said
insulated conductor relative to said point of reference and for
mounting said monitoring circuit means on said opposite end of said
conductor.
35. An article of manufacture for monitoring the level of an
electrically conductive liquid in a container, comprising in
combination:
means for electrically monitoring the level of said liquid
including an elongate electric conductor having a length, relative
to a point of reference, greater than the distance between said
point of reference and a predetermined low level of said liquid,
being electrically insulated for a length which, relative to said
point of reference, is greater than said distance, and being
reducible to a length equal to a distance between said point of
reference and said predetermined low level to provide an end of
said conductor free of electric insulation at said predetermined
low level of said liquid and electric monitoring circuit means
connected to an end of said conductor opposite said free end;
and
means connected to said insulated conductor for mounting said
insulated conductor relative to said point of reference and for
mounting said monitoring circuit means on said opposite end of said
conductor.
36. An article as claimed in claim 34 or 35, including:
a protective tubular coating covering part of said electric
insulation.
37. An article as claimed in claim 34 or 35, including:
a stopper surrounding said elongate insulated electric conductor
remotely from said free end.
38. An article as claimed in claim 37, wherein:
said stopper has a taper extending in the direction of said free
end.
39. An article as claimed in claim 37, wherein:
said stopper is adjustable along part of said elongate insulated
electric conductor.
40. An article as claimed in claim 34 or 35, wherein:
said mounting means include means for mounting said monitoring
circuit means at said point of reference.
41. An article as claimed in claim 34 or 35, including:
a conductor enclosing said electric monitoring circuit means on
said end of said conductor opposite said free end.
42. An article as claimed in claim 34 or 35, wherein:
said means including said elongate electric conductor have
sufficient stiffness to carry said monitoring circuit means at said
opposite end.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The subject invention relates to condition responsive indicating
systems and, more specifically, to methods and apparatus for
electrically or electronically monitoring liquid levels, with
particular reference to liquids having volume resistivities in the
megohm-centimeter range.
2. Disclosure Statement
This disclosure statement is made pursuant to the duty of
disclosure imposed by law and formulated in 37 CFR 1.56(a). No
representation is hereby made that information thus disclosed in
fact constitutes prior art inasmuch as 37 CFR 1.56(a) relies on a
materiality concept which depends on uncertain and inevitably
subjective elements of substantial likelihood and reasonableness,
and inasmuch as a growing attitude appears to require citation of
material which might lead to a discovery of pertinent material
though not necessarily being of itself pertinent. Also, the
following comments contain conclusions and observations which have
only been drawn or become apparent after conception of the subject
invention.
By way of example, and not by way of limitation, the subject
invention may profitably be considered against the background and
in the context of lubrication oil level monitoring systems for
automotive engines.
In this respect, the currently standard and almost universal
technique of checking lubrication oil levels in automotive engines
requires the performance of several manual steps which typically
cannot be carried out without physical exertion and soiling of
hands, and which involve the release and elevation of the engine
hood, removal and wiping of the oil dipstick, reinsertion of the
wiped dipstick into and through a narrow tube, renewed removal of
the thus reinserted dipstick, inspection of an oil deposit on the
dipstick in relationship to graduated markings near the dipstick
end, reinsertion of the dipstick into the dipstick tube, and
reclosure of the engine hood, sometimes after addition of
lubrication oil, such as may be necessary.
The tediousness of this low-technology approach involves the risk
that oil checks may not be carried out with sufficient frequency as
to assure detection of dangerously low oil levels from which severe
engine damage can easily result. The current proliferation of
self-service stations and a general lessening of station attendant
service, accelerated in some parts by gas shortage phenomena, have
considerably aggravated the problem.
It would thus be highly convenient and advantageous to have an oil
level monitoring system that would be easily and reliably
surveyable from the driver's seat of an automobile. Existing
proposals, unfortunately, fell short of this goal.
In particular, the rain alarm of U.S. Pat. No. 1,285,986, with its
interdigitated electrode sets, battery-operated bell and canvass
canopy, obviously would be ill-suited for a level monitoring
device. The disclosure of U.S. Pat. No. 2,624,790 represents a
thirty-year-old attempt to replace an automobile engine dipstick by
an automatic device. To this end, an auxiliary pump having its
intake at the low-oil level was employed to pump oil to an electric
pressure sensing device, as long as there was sufficient oil in the
crankcase. In practice, this approach would have called for
expensive extra equipment of a relatively delicate nature.
Similar considerations apply to a proposal according to U.S. Pat.
No. 2,688,251, which employs manifold vacuum for operating a
pneumatic oil level indicating system.
The liquid level detector proposal according to U.S. Pat. No.
2,792,566 energizes two electrodes of unequal lengths with direct
current and with alternating current, respectively, to indicate
different liquid levels through the glowing of both or only one
electrode of a gas-discharge lamp. In practice, application to the
oil being monitored of the relatively high voltage needed for the
operation of such a lamp would have created a fire hazard. Similar
considerations apparently dictated the construction of the elongate
tube housing the electrodes of glass or plastic, which would have
been ill-suited for an automotive engine environment.
The same in effect applies to the electroluminescent liquid level
indicator proposed in U.S. Pat. No. 3,038,097.
U.S. Pat. No. 3,054,291 proposes an illuminated liquid gage in
which oil in the crankcase uncovers a color line when the oil level
reaches a low level, so as to change the hue of a signal light
transmitted through a transparent rod to the dashboard. In
practice, such transmitted light is difficult to observe in
daylight. Also, the light guide probe will in practice become
covered by an oil film, whereby the system will erroneously
indicate a sufficient oil level even after the oil has receded to
dangerously low levels. The materials suggested for that light
transmitting gage moreover are vulnerable to the engine heat and to
hot oil vapors.
The proposal of U.S. Pat. No. 3,181,361 employing a spark gap probe
energized by a high-voltage transformer and operated via a cable
and pulley suspension, is at best suitable for stationary
installations and non-flammable liquids, such as molten glass.
Liquid level indicators of the type proposed in U.S. Pat. No.
3,350,710 determine the presence and absence of liquids by means of
a temperature sensing technique. One problem with such systems is
an inherent time delay in conflict with the need to provide the
driver with a quick indication upon his actuation of the indicator
actuation button. In an attempt to alleviate this problem, the
proposal according to that patent suggests that a very fine wire of
high temperature coefficient material be immersed into the
particular liquid, which is supposed to keep the immersed wire
relatively cool. The wire is positioned such that the liquid level
will sink below the wire when the liquid level reaches a low value.
In that case, the electrically heated wire is supposed to rise
rapidly in temperature because of a lack of a heat sink through the
particular liquid.
In fact, the heat developed by the passage of electric current is
made sufficient to evaporate any liquid from the wire at that
stage. This is, however, a rather dangerous practice, particularly
in engine crankcase environments containing oil vapors. Also, a
cooling effect through heat of evaporation would appear to
introduce a time delay of its own as far as the electrically heated
wire is concerned. A related system which relies on the temperature
dependence of the resistivity of silicon to differentiate between
the presence or absence of a liquid, such as lubrication oil, has
been described in an article entitled Sensors Respond to Fluid
Level, having appeared in ELECTRONICS, July 5, 1979, pp. 53 to
56.
British Patent Specification No. 1,130,621 proposes the use of two
bare electrodes of equal lengths in a water sensor employed in
water tanks and overflow pipes of individual units in
multi-apartment dwellings. In practice, bare electrode systems
would be difficult to implement in an engine crankcase or similar
environment, especially if two parallel electrodes of equal lengths
are to be employed, as suggested in this British proposal.
A variation on the theme of the above mentioned U.S. Pat. No.
3,054,291 is apparent from U.S. Pat. No. 3,466,928, which suggests
the use of fiber optics technology for transmitting a crankcase oil
level indication to the dashboard of an automobile. As can be seen
from that proposal, a coherent fiber optics system of high
temperature stability is required in addition to a rather complex
illumination system through the crankcase wall.
Moreover, though the particular proposal suggests a coating of
essential optical parts with fluorinated ethylene-propylene or
other non-wetting material, it appears questionable to what extent
such measures will prevent the optical system over the life of the
engine from becoming obstructed or otherwise affected by oil films
forming on mirror and window surfaces essential to the operation of
the system.
U.S. Pat. No. 3,495,214 proposes a transistorized system with an
electrode probe partially immersed in a liquid and colored lights
at the dashboard for liquid level indication. A problem with this
and similar electrical sensing systems is that they cannot
distinguish in their indication between a satisfactory liquid level
and a failure of the electrode probe insulation. In either case,
the driver will be given the green light in response to his
actuation of the indicator switch, and will thus be led to believe
that the liquid level remains to be satisfactory, even after having
receded to dangerously low levels. In practice, probe insulation
failures are immune to detection through the type of electric
testing procedures proposed in the mentioned U.S. Pat. No.
3,495,214. These problems are further aggravated by an electrode
probe structure in which the electrode is separated from closely
adjacent metallic parts by insulating material which presents
around the electrode an at least practically horizontal surface
extending parallel to and facing the level of the liquid being
monitored. An excessive liquid level will thus tend to leave a
conductive oil deposit between the probe electrode and adjacent
metallic parts, even after the liquid has receded to a normal range
of levels.
This kind of drawback affects also the bare electrode structure
shown in U.S. Pat. No. 3,550,080 and the concentric electrode
structure shown in FIG. 6 of U.S. Pat. No. 3,848,616. That patent
alternatively suggests the use of interdigitated electrodes of the
kind proposed for the rain alarm shown in the above mentioned U.S.
Pat. No. 1,285,986. Those interdigitated electrode structures in
practice are, however, largely insensitive to changes in liquid
level across most of their width or length.
The fluid level sensing probe according to U.S. Pat. No. 3,975,582
has a slender insulating bushing of thermoplastic material extend
along part of a metal electrode and joined to and surrounded by a
thin-walled concentric cup-shaped shell of semirigid plastics
material. In order to mount that probe in operative condition, the
cup-shaped shell is snapped into position at a cylindrical seating
in a hole in the liquid container wall. An alternative proposal
dispenses with the slender insulating bushing in favor of an
extended shell or shroud surrounding part of the electrode. It is
at least questionable to what extent a horizontally mounted probe
as shown in the latter patent will satisfy liquid level monitoring
needs of the type primarily under consideration herein. Also, it
appears that the provision of a hole in the liquid container wall
renders the system vulnerable to sudden loss of the oil or other
liquid being monitored. This problem appears aggravated in the
cited proposal which places reliance for sealing the particular
hole on a snap fit of a semirigid plastic part.
A pneumatic oil level checking device has recently become
commercially available under the designation "OIL CHEK". That
system has a probe in the form of a tube which originally is longer
than the distance from the top of the dipstick tube to the low oil
level. Prior to insertion of that probe into the dipstick tube, the
probe is cut to correspond in length to the regular dipstick of the
particular engine down to the "add oil" mark. Thin tubing
pneumatically connects the probe to a plunger arrangement at the
dashboard or steering wheel column. That arrangement has a piston
which is actuated in a cylinder by the manually actuable plunger,
in order to propel air through the tubing into the probe when the
plunger is depressed. If the oil level in the crankcase has receded
from the free end of the probe, air can enter its longitudinal
passage, whereby the depressed plunger will pop out of the
dashboard or steering column unit. On the other hand, if the free
end of the probe is immersed in oil, air cannot enter the probe
from the free end thereof and the plunger will stay in the checking
unit, indicating to the driver or operator the presence of oil at a
satisfactory level. As a safety against faulty indications in this
respect, the checking unit includes a check button which, when
depressed will cause the plunger or indicator to pop out
immediately. However, no safety check is apparent which would
afford a distinction between air leaks in the system and
insufficient oil levels, except that provisions are made for a use
of the tubular probe in the manner of a conventional dipstick.
A further proposal advanced by one of the subject coinventors
provides an electronic dipstick in the form of an elongate base
member having a pair of leads with spaced terminals located
thereon.
The base member is of electrically insulating material, or the
leads and terminals are otherwise insulated from each other. Liquid
present at a satisfactory level will bridge the spaced terminals,
thereby permitting flow of an electric indicating current. On the
other hand, liquid receding to an insufficient level will leave the
terminals in an open-circuit condition. Two pairs of terminals may
be employed for an indication of high, medium and low liquid
levels. A conical stop element tapering in a direction toward the
upper end of the elongate base member is slidable along that base
member, has a set screw for releasably securing such stop element
to the base member according to the length of the dipstick
receiving tube, and has a second screw disposed to releasably bear
against the outer surface of the dipstick receiving tube to prevent
lifting of the base member out of that tube.
Such type of electronic dipstick appears exposed to the danger of
residual oil films and contamination deposits bridging the spaced
terminals on or at the base member, and thereby causing the
provision of a faulty indication, even after the liquid or oil has
receded to an insufficient level. This problem appears aggravated
in the case of engine oils which have a high volume resistivity in
the megohm-centimeter range, comparable to the resistivity of
residual oil or contaminant films.
On the subject of slidable stop members, it is mentioned that there
are so-called "universal" conventional dipsticks having a stop
member adjustable along the dipstick rod or blade.
SUMMARY OF THE INVENTION
It is a general object of this invention to overcome the
disadvantages and satisfy the needs expressed and implicit in the
above disclosure statement and in other parts hereof.
It is a germane object of this invention to provide improved
methods and apparatus for monitoring the level of a liquid,
particularly of an electrically conductive liquid.
It is a related object of this invention to provide improved
methods and apparatus for monitoring liquids of high-volume
resistivity, typically in the megohm-centimeter range.
It is also an object of this invention to immunize monitoring
methods and apparatus against dangerous and costly
malfunctions.
It is a related object of this invention to provide improved
monitoring methods and apparatus which in practice are insensitive
to liquid or oil level variations above the lowest satisfactory
level.
It is also an object of this invention to provide electronic
dipsticks and similar articles of manufacture for monitoring the
level of electrically conductive liquids.
Other objects will become apparent in the further course of this
disclosure.
From a first aspect thereof, the subject invention resides in
methods and apparatus for monitoring the level of electrically
conductive liquid wherein the length of an electrically insulated
conductor is diminished or otherwise adjusted with respect to a
given point of reference and a predetermined low liquid level.
According to a preferred embodiment of the invention, an elongate
electric conductor is provided with a length, relative to a point
of reference, greater than the distance between such point of
reference at a predetermined low level of the liquid to be
monitored. The elongate conductor is electrically insulated by
providing such elongate conductor with electric insulation for a
length which, relative to the mentioned point of reference, is
greater than the mentioned distance. This, in practice, enables an
installer or customer to adapt the length of the insulated
conductor to the requirements of a particular engine, by cutting
the conductor and its electric insulation at the mentioned
predetermined low liquid level to diminish the length of the
insulated conductor with respect to the point of reference to a
length equal to the mentioned distance and by providing the
conductor at a position corresponding to the predetermined low
level relative to the point of reference with an end free of
electric insulation. The user then inserts the insulated conductor
of diminished length into the container of the liquid to be
monitored, to position the free end of the conductor at the
location of the predetermined low level. The subject embodiment of
the invention then electrically monitors the level of the liquid
with the inserted insulated conductor exposed to the electrically
conductive liquid at its free end.
From a related aspect thereof, the subject invention resides in
methods and apparatus for monitoring liquids having volume
resistivities in the megohm-centimeter range, with the aid of an
elongate electric conductor having a free end at a position
corresponding to a predetermined low-liquid level.
According to an embodiment of the subject invention, electric
monitoring circuit means are connected to and mounted on the
elongate electric conductor at an end opposite the mentioned free
end.
Other aspects of the subject invention, and clarifications and
elaborations on statements so far made, will become apparent from
the description of preferred embodiments set forth below in
conjunction with the drawings. This relatively brief summary of the
invention is neither intended as a substitute for the claims of
this application nor as a limiting influence on the ultimately
granted patent rights.
BRIEF DESCRIPTION OF THE DRAWINGS
The subject invention and its various aspects and objects will
become more readily apparent from the following detailed
description of preferred embodiments thereof, illustrated by way of
example in the accompanying drawings in which like or functionally
equivalent parts are designated by like reference numerals, and in
which:
FIG. 1 is a diagrammatic front elevation, in section, of an
automotive engine equipped with an electronic dipstick according to
a preferred embodiment of the subject invention;
FIG. 2 is an elevation, on an enlarged scale, of the end of a
conventional dipstick, shown for the purpose of comparison and
explanation;
FIG. 3 is a side view of an electronic dipstick device and of an
illustration of its adjustment to a useful length, in accordance
with an embodiment of the subject invention;
FIG. 4 is a side view of an adjustable electronic dipstick in
accordance with a further embodiment of the subject invention;
FIG. 5 is a detail view on an enlarged scale of the type of
electronic dipstick shown in FIGS. 1, 3 and 4;
FIG. 6 illustrates a modification of the embodiment shown in FIG.
5, in accordance with a further embodiment of the subject
invention; and
FIG. 7 is a diagram of a monitoring circuit for use with the
dipsticks of FIGS. 1, 3, 4, 5 and 6, in the best mode currently
contemplated of carrying out the subject invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
The automotive engine 10 shown in FIG. 1 has a metal container 12
attached thereto, including the familiar crankcase sump 13.
The sump 13 contains lubricating oil 14 which is circulated by an
oil pump (not shown) via a strainer 15 and oil pipe 16, to return
to the sump, typically by force of gravity, upon lubrication of
various engine parts, and passage through an oil filter. In
accordance with standard practice, the supply of lubricating oil 14
in the sump 13 may be replenished through a top opening normally
closed by a removable cap 18.
A dipstick tube 19 extends through a wall 20 of the engine. In
particular, the tube 19 extends from the outside of the container
12 or of the engine 10 from above the liquid 14 to an end 21 of the
tube inside the container 12 or at any rate inside the container
enclosing the oil sump and engine crankcase.
The metallic or electrically conductive tube 19 is electrically
connected to the container 12 via the engine wall 20, for
instance.
An elongate electric conductor 22 (see FIG. 3) is extended through
the tube 19 into the liquid 14 and has or is provided with a free
end 23 at a position corresponding to a predetermined low level of
the liquid 14. In this respect, reference may be had to FIG. 2,
showing an end portion of a conventional dipstick 25 provided with
markings showing a satisfactory oil level and indicating also an
unsatisfactory or insufficient level. In particular, the
designation FULL indicates a satisfactory oil level.
The legend ADD 1 QT indicates an unsatisfactory or low level, while
the optional word SAFE designate a range within which the oil level
may vary. By way of example, the free end 23 of the conductor 22
may in its inserted position be located at the level of the mark
associated with the legend ADD 1 QT on the dipstick end portion
shown in FIG. 2.
An electronic dipstick according to the subject invention is
employed in lieu of the conventional dipstick 25 as shown, for
instance, in FIG. 1. The electronic dipstick 26 thus shown includes
an electric insulation 27. In particular, the insulation 27 extends
along the conductor 22 in the tube 19 and isolates the free end 23
of the conductor from the tube 19 below the tube end 21.
The latter isolation of the free conductor end 23 from the tube end
21 is an important feature of the currently discussed aspect of the
subject invention. In particular, the invention thus avoids the
drawbacks of the above mentioned proposals in which conductive oil
deposits were left between the probe electrode and adjacent
metallic parts, even after the oil or other liquid had receded to a
normal range of levels or to an unsatisfactory low level. In
addition to the electrical insulation provided at 27, the extension
and arrangement of the insulation also afford a physical isolation
of the probe end 23 from metallic parts. It will be noted in this
respect that the insulation 27 between the metal tube 21 and probe
end 23 extends at an acute angle to the vertical, thereby promoting
the flowing off or removal of an oil film which may accidentally be
formed between the tube end 21 and probe end 23 during the
operation of the engine or in case of an overfill condition. If
desired, the insulation 27 between the metal tube 21 and probe end
23 may in fact extend vertically or perpendicularly to the liquid
or oil level or surface.
The electronic dipstick 26 is operated with the aid of a monitoring
circuit 29 having an input terminal 31 and a ground terminal 32
(see FIGS. 3 and 7). The input terminal 31 of the monitoring
circuit 29 is electrically connected to the conductor 22 outside of
the electrically conductive container 12, in a bottom region of
which the oil or liquid 14 is located. The ground terminal 32, on
the other hand, is electrically connected to the container 12, as
diagrammatically indicated in FIG. 7.
In apparatus for monitoring the level of an electrically conductive
liquid 14 in a container 12, the subject invention in its currently
discussed embodiment thus provides an improvement comprising, in
combination, an elongate electric conductor 22 extending into the
container 12 and having a free end 23 exposed to the liquid 14,
electric insulation 27 covering the conductor 22 up to its free end
23, and means 29 connected to the conductor 22 remotely from the
free end 23 for electrically monitoring the level of the liquid 14
with the conductor 22 covered by the electric insulation 27 and
exposed to the electrically conductive liquid at the mentioned free
end 23.
Similarly, with specific reference to FIG. 1, a preferred
embodiment of the subject invention provides apparatus for
monitoring the level of an electrically conductive liquid 14 having
typically a volume resistivity in the megohm-centimeter range and
being located in an electrically conductive container 12.
More specifically, this preferred embodiment resides in the
improvement comprising, in combination, an electrically conductive
tube 19 electrically connected to the container 12 and extending
from outside of the container 12 from above the liquid 14 to an end
21 of the tube inside the container, and an elongate electric
conductor extending through the tube 19 into the liquid 14 and
having a free end 23 at a position corresponding to a predetermined
low level of the liquid 14. As part of this combination, electric
insulation 27 extends along the conductor 22 in the tube 19 and
below the end 21 of that tube into the liquid 14 to isolate the
free end 23 of the conductor 22 from the tube 19, as explained
above. As a further part of this combination, monitoring circuit
means 29 have an input terminal 31 electrically connected to the
conductor 22 outside of the container 12 and a ground terminal
electrically connected to that container.
According to the embodiment shown in FIG. 3, the subject invention
provides an elongate electric conductor 22 with a length 34,
relative to a point of reference 35, greater than the distance 36
between that point of reference and a predetermined low level 37 of
the liquid 14 to be monitored. The invention according to this
embodiment also electrically insulates the elongate conductor for a
length which, relative to the point of reference 35, is greater
than the distance 36. For instance, the invention according to this
embodiment may provide the conductor 22 with electric insulation 27
for the length 34 of the conductor 22 as seen from the point of
reference 35.
This embodiment of the invention then adjusts the length of the
insulated conductor with respect to the point of reference 35 to a
length equal to the distance 36 and provides the conductor at a
position corresponding to the predetermined low level 37 relative
to the point of reference 35 with an end 23 free of electric
insulation 27 as shown in FIG. 1. The resulting insulated conductor
22 of diminished length 36 is then inserted into the container 12
to position the free end 23 at the location of the mentioned
predetermined low level 37. The actual level of the liquid 14 is
then electrically monitored with the inserted insulated conductor
22 exposed to the electrically conductive liquid 14 at the free end
23.
According to a related embodiment thereof, the subject invention
provides an article of manufacture for monitoring the level of an
electrically conductive liquid 14 in a container 12. The article of
manufacture according to this embodiment comprises means for
electrically monitoring the level of the liquid 14, including an
elongate electric conductor 22 having a length 34 (see FIG. 3),
relative to a point of reference 35, greater than the distance 36
between that point of reference and a predetermined low level 37 of
the liquid 14. The conductor 22 of that article of manufacture is
electrically insulated for a length, such as the above mentioned
length 34, which, relative to the point of reference 35, is greater
than the distance 36. Moreover, the insulated conductor in that
article of manufacture is reducible to a length equal to a distance
36 between the point of reference 35 and the predetermined low
level 37, to provide an end 23 of the conductor 22 free of electric
insulation 27 at the predetermined low level 37 of the liquid
14.
The article of manufacture under consideration further includes
means, such as a flange 39, connected to the insulated conductor 22
and 27 for mounting such insulated conductor relative to the point
of reference 35.
By way of example, and as seen in FIGS. 4 and 5, the electronic
dipstick according to an embodiment of the invention may have a
protective tubular coating 41, covering part of the electric
insulation 27. In particular, the protective tubular coating 41 may
be connected to the flange 39 which, in turn, preferably supports a
can or container 42 housing at least part of the monitoring circuit
29.
In practice, the tubular coating 41 at least partially extends into
the tube 19, thereby protecting the insulator 27 against chafing
and other deleterious exposure at the upper end of the dipstick
tube 19. To this end, the protective tubular coating 41 and the
flange 39 are preferably manufactured of a durable metal or other
tough, temperature-resistant material.
The electric insulation 27 typically is of a mechanically tough,
temperature-resistant material of high electric resistance and a
certain flexibility to accommodate bends in the dipstick tube 19.
By way of example, suitable materials for the electric insulation
27 of the conductor 22 include polytetrafluorethylene (Teflon),
polypropylene, and polyimide plastics. These materials are also
reducible to the desired length 36, such as by means of a knife,
saw blade or similar cutting instrument indicated at 44 in FIG.
3.
The reference point symbolized by the line 35 in FIG. 3 may, for
instance, be the upper free end or top 45 of the dipstick tube 19,
as shown in FIG. 1. That, in practice, corresponds to the innermost
surface 46 of a cap 47 that is conventionally attached to a regular
dipstick 25, as shown in FIG. 3. Prior to installation of an
electronic dipstick according to an embodiment of the subject
invention, the installer or customer may adapt the length thereof
to the requirements of the particular engine.
In particular, the installer may use the existing dipstick as a
guide, placing the innermost surface 46 of the cap 47 at the level
of the reference point 35 or, for instance, of the lower surface of
the flange 39. The installer may then take a tool 44 as shown in
FIG. 3 and cut the conductor 22 and insulation 27 at a
predetermined low liquid level 37 which may, for instance, be the
ADD 1 QT mark of the dipstick 25 (see FIG. 2). If desired or
necessary, a knife or similar instrument may be employed to recess
the insulation 27 for a short distance at the free end 23 of the
conductor 22 without, however, impairing the above mentioned
isolation of the free end 23 from metallic parts, including the
dipstick tube 19. Depending on the nature of the tool 44 used for
cutting the insulation 27, such short recess at the free end 23 may
be formed automatically, as in the case of insulation strippers
employed for removing insulation from electrical wires. At any
rate, provision of a short recess of the insulation has the
advantage of precluding obstruction of the free conductor end 23 in
case the insulation 27 should elongate itself somewhat on the wire
22, such as due to temperature or stress conditions.
The diminishing of the length of the insulated conductor as shown
in FIG. 3 is one way in which the length of the insulated conductor
22 and 27 may be adjusted to the dimensions or requirements of a
particular engine or other liquid container. Another way according
to an embodiment of the invention includes the provision of a
movable member defining the point of reference 35 as, for instance,
in the case of certain universal oil dipsticks, and the setting of
that movable member at the insulated conductor at the distance 36
from the free end 23. In that case, the free end 23 may be provided
on the electronic dipstick at the factory.
With particular reference to FIG. 4, it is seen that the elongate
insulated electric conductor is surrounded at or about the point of
reference 35 with a movable member or stopper having a setting
member or set screw 49. The protective tubular coating 41 is
preferably provided on the insulated electric conductor 22 and 27
over the range of movement of the movable member or stopper 48.
The movable stopper 48 shown in FIG. 4, as well as the stationary
stopper 51 shown in FIG. 6, are examples of members for covering
the end 45 of the dipstick tube 19, opposite the end 21 inside the
container 12, around the electric conductor 22. Such coverage or
closure of the upper free end 45 of the dipstick tube according to
the currently discussed embodiment of the subject invention
represents an important feature, especially in the case of
automotive engines or in the case of other applications where no
liquid or vapor must escape from the dipstick tube.
By way of example, environmental protective laws and regulations
require automotive engines to be equipped with positive crankcase
ventilation [PVC]. In such ventilation systems, the intake manifold
vacuum is employed to draw fumes out of the crankcase for
application to the engine cylinders where such gases will be burnt
along with the regular fuel charge. Sealing or closure of the
dipstick tube 19 around the electronic dipstick according to an
embodiment of the subject invention will not only avoid impairment
of the positive crankcase ventilation through undesired entry of
air via the dipstick tube, but will also prevent an escape of fumes
or oil through the free tube end, such as in the case of
conventional modern dipstick devices.
The movable stopper 48 or the stationary stopper 51 surrounding the
insulated electric conductor is inserted into the upper end 45 of
the tube 19 opposite the end 21 inside the container. The stopper
may in particular be provided with a taper extending into the tube
19. This taper may, as shown in FIG. 6, be designed to fit into a
corresponding taper of a flared end 52 of the tube 19. In other
words, the stopper 48 or 51 extends in the direction of the lower
free tube end 21, but is inserted into the upper free tube end 45
or 52.
The adjustable movable member defines the point of reference 35,
such as by a surface similar to the innermost surface 46 of the cap
47 if that kind of adjustable member is employed, or by virtue of
its maximum penetration into the straight or flared tube end if the
movable member is a tapered or frusto-conical stopper.
By way of example, FIG. 4 shows a minor circle 54 of the tapered
stopper 48 as defining the point of reference 35 relative to the
free probe end 23. This minor circle 54 may, for instance,
correspond to the uppermost end of the dipstick tube 19.
The movable member of stopper 48 is adjusted relative to the free
probe end 23 until the distance between such free probe end and the
reference circle 54 is equal to the above mentioned distance 36;
the purpose of such relative adjustment being to provide an
indication as more fully described below, when the oil or other
liquid 14 has receded to an unsatisfactory level.
As the article of manufacture shown in FIG. 3, the electronic
dipstick illustrated in FIG. 4 also has a length greater than the
desired distance 36 between the point of reference 35 and a
predetermined low level 37 of the liquid. In particular, the point
of reference 54 indicated in FIG. 4 moves along with the adjustable
member 48, so that the length of the elongate electric conductor,
relative to the point of reference 54, initially is actually or
potentially greater than the desired distance 36, until the movable
member 48 has been set at its proper position for the particular
engine.
In general, the embodiment of FIG. 4 presents an article of
manufacture for monitoring the level of an electrically conductive
liquid in a container.
This article of manufacture comprises, in combination, means for
electrically monitoring the level of the liquid 14, including an
elongate electric conductor having a length, relative to a point of
reference 54, greater than the distance 36 between the point of
reference 35 and a predetermined low level 37 of the liquid 14.
Also, the elongate conductor is electrically insulated for a length
which, relative to the point of reference 54, is greater than the
distance 36, and is adjustable to a length equal to that distance
36 between the point of reference 35 and the predetermined low
level 37 to provide an end 23 of the conductor free of electric
insulation 27 at that predetermined low level 37 of the liquid 14.
The stopper 48 in the embodiment of FIG. 4 then presents means
connected to the insulated conductor for mounting the insulated
conductor relative to the point of reference 35. This is done in
the embodiment of FIG. 4 by rendering the stopper 48, which defines
a reference point 54, adjustable relative to the elongate insulated
electric conductor.
The embodiment of FIG. 4 is particularly advantageous if a manifold
or other source of heat adjacent to the dipstick tube would
adversely affect the monitor circuitry in the can 42. In that case,
the can 42 with enclosed monitor circuitry may be considered
adjustable relative to the reference point 35 or 54 or free tube
end 45 or 52, by virtue of the stopper 48 with set screw 49.
In other words, the embodiment of FIG. 4 enables the can 42 with
enclosed monitor circuitry 29 to be positioned at a safe distance
from any source of heat or other adverse influence. In this
respect, the features of FIG. 3 including an initially excessive,
diminishable length of the insulated conductor, and of FIG. 4,
including the adjustability of the reference point 54, may be
combined in one and the same electronic dipstick for an increased
universality of its utility in various engine or liquid container
types under various thermal and other environmental
circumstances.
According to a preferred embodiment of the subject invention, the
electrical monitoring or at least a substantial part thereof is
effected at an end of the insulated conductor opposite its free end
23. In terms of FIGS. 1 and 3 to 7, the electrical monitoring
function is performed at the top of the electronic dipstick.
The monitoring circuit and its container 42 are thus preferably
supported at the upper end 55 of the elongate electric conductor
opposite its free end 23. To this end, the electric conductor
according to an embodiment of the subject invention is sufficiently
stiff to carry the monitoring circuit means 29 and 42.
This is particularly important if the electronic dipstick is
adjustable as in FIG. 4, whereby the can 42 with enclosed
monitoring circuit may be located at a distance from the adjustable
member 48 and dipstick tube 19.
On the other hand, the protective coating or tube 41, flange or
baseplate 39, or stopper 48 or 51 may serve as means for mounting
the monitoring circuitry on an end 45 of the dipstick tube 19
opposite its end 21 inside the container 12. In the alternative,
the flange or baseplate 39, the protective coating or tubular
member 41 or the tapered stopper 51 may serve as a means for
mounting the monitoring circuitry on or at an end of the elongate
conductor 22 opposite its free end 23.
If desired, the monitoring circuitry may be located closer to or at
the dashboard of the vehicle and may be connected to the dipstick
conductor by a preferably shielded cable; provided no undue
interference is picked up thereby. To avoid such danger, the
electronic circuitry for the dipstick may be composed of two parts,
namely a monitor circuit 29 preferably enclosed in the can 42 and
an indicator unit 61 mounted on or about the dashboard of the
particular vehicle or at a control panel in the case of a
stationary engine.
The monitor circuit 29 is connected to the indicator unit 61 via a
cable 62 and connector 63 including connector elements 64 for the
ground 32, 65 for a voltage supply 66 and 67 for an output of the
monitor circuit 29 and input of the indicator unit 61. The ground
32 may be either connected directly to the monitor circuit 29 as
shown in FIG. 7, or indirectly via the connector element 64. In
either case, the monitor circuit 29 and indicator unit 61 have a
common ground via the connector element 64, and such ground is also
common with the liquid container 12 via the engine frame and other
metallic parts of the particular vehicle.
The monitor circuit 29 includes an operational amplifier 71 having
an inverting input 72 and a noninverting input 73 connected to a
bridge circuit 74.
The bridge circuit 74 is energized from a voltage divider including
resistors 75 and 76 connected between the positive voltage supply
and ground so as to appropriately reduce the supply voltage which,
in practice, may be the battery voltage of the particular vehicle
or engine installation.
The bridge circuit includes a first leg comprising resistors 77 and
78 connected in series between the junction of the voltage divider
resistors 75 and 76 and ground. This provides a reference voltage
for the operational amplifier at a junction 79 between the bridge
resistors 77 and 78. The junction 79 is connected via a resistor 81
to the inverting input 72 of the operational amplifier 71. The
resistors 78 preferably has a resistance several times higher than
the resistor 77, so that most of the voltage appears across the
resistor 78.
The second leg of the bridge circuit 74 has a resistor 82 and such
resistance as present between the probe 22 and grounded container
12. A junction of the probe 22 and resistor 82 is connected to the
non-inverting input 73 of the operational amplifier 71. In the
embodiment illustrated in FIG. 7, it is the input terminal 31 of
the monitor 29 that is connected to the operational amplifier input
73.
A significant advantage of the illustrated circuitry is that the
resistor 82 can have a very high value, such as into the onehundred
megohm range, whereby any arcing at the probe end 23 is
precluded.
This stands in favorable contrast to prior-art proposals in which
no safeguard against electric arcing was provided. Of course, any
electric spark or undue heat development in the engine crankcase or
in other environments containing combustible liquids and fumes
should be strictly avoided.
The monitoring and level sensing equipment herein shown in
compliance with best mode requirements is suited to operation with
liquids having volume resistivities in the megohm-centimeter range.
This in contrast to prior-art proposals, in which lubricating oils
and other high-resistivity liquids were considered or in fact
operated as electric insulators, rather than conductors.
The output of the operational amplifier 71 is connected via the
connector element 67 and an indicator input 84 to bases of driver
transistors 85 and 86 in the indicator unit 61. These transistors
85 and 86 are connected in series between the positive voltage
supply and ground and are of the NPN and PNP type,
respectively.
Two light-emitting diodes 87 and 88 are connected in parallel
between the junction between transistors 85 and 86 and the junction
between resistors 91 and 92 connected in series between the
positive power supply and ground.
Operation of the electronic dipstick is initiated by depression of
a push button 93 which temporarily connects the circuitry 29 and 61
to the power supply 66.
This applies electric current to the bridge 74 via voltage divider
75 and 76 and also energizes the operational amplifier 71 which
thus commences to act as an electric current or voltage
comparator.
In particular, if there is no oil in the crankcase, or if such oil
has receded to a level below the free end 23 of the probe 22, the
resistance between the terminals 31 and 32 is practically at
infinity and the operational amplifier 71 applies a high output to
the indicator input 84. This turns on the NPN transistor 85, while
turning off the PNP transistor 86. Accordingly, the red light
emitting diode 87 is energized and by its display to the driver or
operator indicates a deficiency, namely the deficient oil condition
in this instance.
On the other hand, if the button 93 is depressed while part of the
probe 22 is immersed in the oil 14, then the terminal 31 and input
73 of the operational amplifier 71 see a resistance considerably
less than infinity. By way of example and not by way of limitation,
the resistance through the oil between the container 12 and probe
22 may be, say, one-thousand megohms in the case of typical
lubricating oils. If the power supply 66 is a 12 volt battery, the
voltage at the amplifier input 73 may then be about 7.7 volts,
while the voltage at the reference input 72 may be 9.12 volts, for
instance. This causes the operational amplifier 71 to apply a low
output to the indicator input 84, turning off the NPN transistor
85, while turning on the PNP transistor 86. In consequence, the
green light emitting diode 88 is energized and turns on, while the
red diode 87 is maintained off.
The operator or driver is thus apprized of the crankcase oil level
condition upon each depression of the push button 93.
The subject invention and its various embodiments may, of course,
be employed for monitoring liquids other than lubricating oils. In
these cases, the extension of the insulation down to the free end
23 of the conductor or probe 22 not only has the advantage of
isolating the probe effectively from adjacent metallic parts, such
as the tube 19 as mentioned above, but also enables the probe to
see an oil resistance largely unaffected by the degree of immersion
of the probe into the oil 14 or other liquid being monitored. This
may be particularly important for a reliable monitoring of
high-resistivity liquids and oils where extremely sensitive
monitoring equipment could unduly respond to resistance
fluctuations due to variations in the degree of probe
immersion.
Though the electronic dipsticks or probes shown in FIGS. 1 and 3 to
6 are highly advantageous for various purposes, it should be
understood that the circuitry according to FIG. 7 has utility with
other kinds and types of probes.
Also, the resistor component 77 may in practice be saved and
dispensed with if the junction 79 is directly connected to the
lower end of the resistor 76, as shown by the dotted line 80,
whereby the resistors 75, 76 and 78 form a voltage divider, with
the lead 80' between the lower ends of the resistors 76 and 78
being omitted in that case.
By way of example, the component 71 in the monitor circuit 29 may
be a wide bandwidth JFET input operational amplifier of the type
LF351 as shown and described, for instance, in the brochure
entitled "LF351 Wide Bandwidth JFET Input Operational Amplifier,"
by National Semiconductor Corporation (1977).
The subject extensive disclosure will suggest and render apparent
to those skilled in the art various modifications and variations
within the spirit and scope of the subject invention.
* * * * *